Solid propellant composition of improved ignitability containing copper manganite as catalyst



United States Patent SOLID PROPELLANT COMPOSITION OF IM- PROVED IGNITABILITY CONTAINING COP- PER MANGANITE AS CATALYST Mark Hoffman, Phillipsburg, N.J., assignor to Chas. Pfizer & Co., Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 16, 1965, Ser. No. 448,892 4 Claims. (Cl. 149-19) This invention relates to a method for promoting ignition, and more particularly to a method for catalytically promoting the ignitability of solid propellant compositions by the use of copper manganite.

As a result of the demanding schedule of our present Space program and the complexities it presents, the need for greater refinement in all phase of space technology becomes necessary. For example, more powerful rocket fuels are constantly being sought to deliver a greater thrust. In this connection, ignition promotors play a most important role. Further, since a number of satellite orbiting missions have failed because of upper stage ignition failure, their importance is greatly emphasized. Ignition generally refers to the process of energy transfer to the propellant from an external source and from exothermic reactions of propellant constituents which causes the temperature of the surface region to increase to the point where combustion is self-supporting. The primary purpose of the energy transport process of the igniter is to raise the surface temperature of the propellant. If the net transfer of energy is sufficient to continue to raise the surface temperature to that required for sustained combustion, the chain of events will lead to successful ignition. Conversely, if at a particular environmental pressure, insufficient energy is supplied by the initial external stimulus, heat losses will outweigh heat gains and sustained combustion will not be achieved.

It is an object of the present invention to provide a new and improved method for promoting ignition. A further object is to provide a new and improved method for promoting ignitability of solid propellants without undue sacrifice of burning rate enhancement. Still another object is to provide a novel ignition composition.

The linear burning rate of propellant and the manner in which the burning rate depends on the intrinsic properties of the propellant and on the conditions under which it is burned are factors of the greatest importance in determining the suitability of the propellant for jet propulsion applications.

The method of determining burning rates is provided by the strand burning technique wherein a long cylindrical propellant strand is ignited at one end in a pressure vessel which has been prepressurized to the desired level with an inert gas. The sides of the strand are covered with a suitable nonexplosive material to prevent the flames spreading along the surface of the grain. Burning takes place at a nearly constant pressure and the burning rate is determined from the direct measurement of the time necessary to burn a measured length of strand.

The novel method disclosed herein for promoting the ignitability of solid propellants comprises incorporating copper manganite into a propellant formulation representative of the preferred type used by the propellant industry wherein said copper manganite is present in an amount to provide from about 0.25 to about 5% by weight of said formulation. More particularly preferred is a composition wherein said copper manganite -is present in an amount to provide from about 0.5% by weight of said formulation.

An example of a solid propellant of the preferred type used by the propellant industry for testing ignition cata- 3,365,337 Patented Jan. 23, 1968 lysts is a 15% PBAN propellant containing 56% ammonium perchlorate having the following composition:

Percent weight Another example of a suitable solid propellant composition comprises from about 50% to about by weight of ammonium nitrate, the remainder consisting of a rubbery copolymer and a curing agent. It should be pointed out, however, that effective ignition promotion utilizing the methods described in this invention, extends and is applicable to all solid propellants.

In accordance with the present invention copper manganite of the empirical formula CuO.Mn ,O having a CuO/Mn O ratio of from 1:1 to 3:1, is prepared by straight-forward procedures well-known to those trained in the art.

For example, copper manganite of the formula CuO.Mn O is prepared by co-precipitating a mixture of copper and manganese hydroxides from an aqueous mixed acid salt solution, washing said precipitate, and calcining said product in a suitable furnace at a temperature of approximately 1100 F. Copper manganite of the formulae 2CuO.Mn O and 3CuO.Mn O are obtained by the addition of manganous chloride to a mixture containing ammoniacal cupric oxide and sodium hydroxide. More particularly, the compound 3CuO.Mn O is isolated when a large excess of copper solution is used.

The method of evaluating copper manganite as an ignition promotor consisted of arc image furnace studies. Ignition of a particular propellant under specific conditions requires a certain minimum amount of energy, defined as the threshold energy. The point of ignition is taken as the first emission of light from the surface of the specimen. By means of high speed motion pictures of the ignition surface, the lapse between the end of the exposure flash and ignition may be measured. Although in the ignition of a rocket motor, energy may be transferred to the propellant surface by convection, conduction, and radiation, the radiation method is preferred since reaction conditions can be more carefully controlled. More specifically, said radiation is effected by means of an electric arc. The time required for a sample to ignite (while maintained under a nitrogen atmosphere) when exposed to a radiant energy flux of 70 caL/cmP/sec. is determined and the results reported as milliseconds of exposure time.

It has now been found that copper manganite of the structure defined above significantly decreased the required ignition time as measured in the arc image furnace. The control and the additives in these studies were generally investigated at levels of 0.5% and 1% by Weight of solid propellant composition. In addition, it has been found quite unexpectedly that copper manganite is a strikingly effective catalyst at levels as low as 0.5%. Further, copper manganite was found to promote ignitability of solid propellants without undue sacrifice of burning rate enhancement.

The following examples are provided by way of illustration and should not be interpreted as limiting the invention, many variations of which are possible Without departing from the spirit or scope thereof.

Epoxy curing system Example I To a solution containing copper sulfate (1 M) and manganese sulfate (2 M) is added a 50% aqueous solution of sodium hydroxide in an amount to provide a 10% excess. The resulting co-precipitated copper and manganese hydroxides are filtered and washed free of any salt by-product, and subsequently calcined in a suitable furnace at a temperature of approximately 1100" F. The calcination product obtained analyzes for copper manganite of the following composition: CuO.Mn O

Example V The ability of copper manganite of the formula CuO.Mn O to be effective as a catalyst at a level as low as 0.5% is demonstrated below in which a comparison is made in strand burning rates for copper manganite compositions at levels of 0.5 and 1%.

l/2% Level 17$ Level Example I] Ignition test data are obtained by conventional arc image furnace studies. The composition containing no additive is compared with those containing copper manganite of the formula CuO.Mn O at levels of 0.5 and 1% and the following results are obtained:

Millisecond Exposure Catalyst Level Time to effect igni- (wt. percent) tion, 0 p.s.i.g.

None l 56. 53:3. 5 Copper manganite 0. 5 38. 5&1. 5 1 50. 53:2. 5

Using a propellant containing no catalyst as the control, the above comparison shows the significant improvement with propellants containing copper manganite at levels between 0.5 and 1%. The basic propellant is a aluminized PBAN propellant containing approximately 65% ammonium perchlorate.

Example III The procedure of Example II is repeated wherein equivalent amounts of copper manganite compounds of the formulas 2CuO.Mn O and 3CuO.Mn O are used in lieu of CuO.Mn O and substantially the same results are obtained.

Example IV is utilized in place of the ammonium perchlorate formulation and substantially the same results are obtained.

650 lobo 1600 860 lqo 2050 Pressure psia.

The above study illustrates the effectiveness of copper manganite as a catalyst at a level of 0.5% by Weight. A 0.5% level shows a burning rate equivalent to 1%.

Example VI The procedure of Example V is repeated wherein equivalent amounts of copper manganite compounds of the formulas: 2CuO.Mn O and 3CuO.Mn O are used in lieu of CuO.Mn O and substantially the same results are obtained.

What is claimed is:

1. In a method for promoting ignitability of solid propellants of the inorganic oxidizer salt type without undue sacrifice of burning rate enhancement, the improvement which comprises incorporating copper manganite of the formula CuO.Mn O having a CuO/Mn O ratio of from 1:1 to 3:1 into a propellant formulation wherein said copper manganite is present in an amount to provide from about 0.25% to about 5% by weight of said formulation.

2. A method as in claim 1 wherein said copper manganite is present in an amount to provide about 0.5% by weight of said formulation.

3. An ignition composition which comprises an intimate physical mixture of copper manganite of the formula CuO.Mn O having a CuO/Mn O ratio of from 1:1 to 3:1 and a solid propellant formulation of the inorganic oxidizer salt type wherein said copper manganite is present in an amount to provide from about 0.25% to about 5% by weight of said formulation.

4. An ignition composition of claim 3 wherein said copper manganite is present in an amount to provide 0.5% by weight of said formulation.

References Cited UNITED STATES PATENTS 2,940,959 6/1960 Rosenthal et al. 25247l X 3,216,954 11/1965 Howk et al. 252-471 X 3,223,653 12/1965 Stiles 252-471 X 3,228,893 1/1966 Stiles 252471 X 3,236,783 2/1966 Stiles 252-471 X CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner.

S. I. LECHERT, 1a., Assistant Examiner. 

3. AN IGNITION COMPOSTION WHICH COMPRISIES AN INTIMATE PHYSICAL MIXTURE OF COPPER MANGANITE OF THE FORMULA CUO.MN2O3 HAVING A CUO/MN2O3 RATIO OF FROM 1:1 TO 3:1 AND A SOLID PROPELLANT FORMULATION OF THE INORGANIC OXIDIZER SALT TYPE WHEREIN SAID COPPER MANGANITE IS PRESENT IN AN AMOUNT TO PROVIDE FROM ABOUT 0.25% TO ABOUT 5% BY WEIGHT OF SAID FORMULATION. 